Field effect transistor with amorphous oxide active layer containing microcrystals and gate electrode opposed to active layer through gate insulator

1. A field effect transistor comprising an active layer of an amorphous oxide containing a microcrystal, wherein a grain boundary interface of the microcrystal is surrounded by the amorphous oxide and a gate electrode formed so as to face the active layer through a gate insulator.

2. The field effect transistor according to claim 1 , wherein the transistor is a normally-off type transistor.

3. The field effect transistor according to claim 1 , which provides a current of 10 microamperes or less between a source and a drain when no gate voltage is applied.

4. The field effect transistor according to claim 1 , wherein the amorphous oxide containing the microcrystal controls entrapment of mobile electrons.

5. The field effect transistor according to claim 1 , wherein the amorphous oxide containing the microcrystal decreases the number of conductive electrons.

6. The field effect transistor according to claim 1 , wherein the amorphous oxide comprised in the active layer has an electron carrier density of less than 10 18 /cm 3 and has a tendency to increase electron mobility as electron carrier density increases.